Polyurethanes have been described as ink additives in U.S. Pat. No. 7,176,248 and U.S. Patent No. 20050176848. In U.S. Pat. No. 7,348,368 polyurethanes are described for use as additives to inkjet ink. In US20080207811 polyurethanes are described as ink additives and the examples use polymerically dispersed pigments. However, none of these describes the combination of colorants and the polyurethanes derived from alkoxy aromatic diols.
In U.S. Pat. No. 6,632,858 polyurethanes are described that are derived from chromophoric groups that have at least one colorant having at least two functional groups selected from isocyanate and isocyanate reactive groups and considered a colored polyurethane.
While inks based on aqueous dispersions with polyurethane additives have provided improved inkjet inks for many aspects of inkjet printing, a need still exists for improved inkjet ink formulations that provide good print quality and good jettability in particular when used in a thermal inkjet printhead. It is known that thermal inkjet printhead has lower tolerance towards the addition of polymer additives on its jettability and reliability compared to piezo inkjet printhead. The present invention satisfies this need by providing compositions having improved optical density, while maintaining other aspects of the ink, dispersion stability, long nozzle life and the like.